This invention relates to systems for lining sewers, tunnels and the like, for restoring sewer or tunnel systems, the original structure of which has degraded over time. The invention particularly concerns a method of manufacturing lining sections.
In the particular example of sewers, the sewer gas hydrogen sulphide reacts to form sulphuric acid, which attacks the mortar within the brickwork of existing sewers. Various lining systems are known, in which a lining is provided within the existing sewer or tunnel system and in which a grout, for example concrete, is introduced into the spacing between the new liner and the original structure.
The resulting sewer or tunnel wall, which comprises the original decaying structure, the grout material and the lining, is subjected to a different distribution of stresses to the original structure. In particular, this change in the stress distribution can result in a large reduction or elimination of the tensile stress in the original wall, which tensile stress typically leads to cracking and crumbling of the original wall, particularly in cases where the mortar of a brickwork structure has been under chemical attack. The level of compressive stresses in the original structure will also be reduced by the introduction of the lining system. The lining also acts as a barrier to prevent further chemical decay of the original structure.
A lining system typically comprises a number of lining sections butted end-to-end in order to form the lining for a sewer system. Each lining section may be a single closed loop or, it may comprise a number of arcuate portions connected together by appropriate joints to form the loop.
This invention is concerned in particular with the manufacture of a lining system in which the material of the lining comprises a sandwich structure having an inner and an outer fibreglass-resin layer, and a sand-resin layer sandwiched between them. A known manufacturing process for the lining is essentially manual, and involves depositing a fibreglass layer of specified thickness over a mould, applying a resin to the fibreglass layer, applying a sand-resin mixture over the fibreglass-resin layer to a desired thickness, depositing a second fibreglass layer of specified thickness over the sand-resin layer, and applying a resin to the second fibreglass layer.
A particular problem encountered in the manufacture of this sandwich structure lies in the control of the thickness of the sand-resin layer. A minimum thickness is specified for the structural properties of the lining. Conventionally, the thickness has been controlled to meet this minimum by using depth gauges, which leave visual tell-tale marks on the surface of the sand resin layer when the desired thickness has been reached or passed. This process is prone to wastage of the sand-resin composition, because the resulting sand-resin layer is thicker than required over most of the area of the structure.
An alternative method of ensuring the desired minimum thickness is obtained involves the use of a tamping device. This is a device which compresses (or displaces) the surface of the sand-resin material using a reciprocating pad, to reach a desired thickness. The sand-resin mixture is intentionally tacky, and indeed it needs to be able to grip to the surface of the underlying fibreglass-resin layer, even against the action of gravity. A problem with this method is that the sand-resin layer can adhere to the tamping pad, and thus become dislodged. Also, due to the essentially incompressible nature of the sand-resin mixture, the tamping process can only achieve the desired thickness for a limited range of depths and only if there is approximately the correct amount of sand-resin mixture to start with.
According to a first aspect of the invention, there is provided a method of manufacturing a sewer or tunnel lining section, comprising:
forming a fibreglass-resin layer over a mould;
applying a sand-resin mixture over the fibreglass-resin layer to a thickness which results in the combined structure having a thickness greater than a preset minimum thickness;
removing sand-resin material from the surface of the sand-resin layer using a wire arranged to lie a predetermined radial distance from the surface of the mould, the wire being passed around the surface of the sand-resin layer whilst maintaining the predetermined radial distance, the predetermined radial distance comprising, or being slightly greater than, the preset minimum thickness; and
forming a second fibreglass-resin layer over the sand-resin layer.
The use of a wire to remove excess sand-resin material has been found to be particularly effective, and surprisingly the excess material does not re-adhere to the underlying surface after the wire has passed. This is despite the required tackiness of the sand-resin mixture.
The first and second fibreglass-resin layers are preferably formed by depositing sheets of fibreglass material and subsequently applying the resin or by spraying particles of fibreglass material to a specified thickness and subsequently applying the resin. Preferably, the mould has a central region where the lining section is formed and side regions which provide guide surfaces, and wherein the wire is arranged to extend between a pair of roller arrangements, the wire being mounted so as to lie a predetermined distance above a surface when the roller arrangements are passed over the guide surfaces.
Each roller arrangement may comprise a single roller, with the wire extending between the two rollers along the axis of rotation of the two rollers or each roller arrangement may comprise two rollers side by side having parallel axes of rotation, the wire being positioned between the two rollers and extending parallel to the axes of rotation of the two rollers between the two roller arrangements.
The invention also provides a method of lining a sewer or tunnel, comprising inserting lining sections of the invention into the sewer or tunnel to form a lining and filling the space between the lining and the wall of the sewer or tunnel with grouting.
According to a second aspect of the invention, there is provided a device for controlling the thickness of a sand-resin mixture in a sewer or tunnel lining section, comprising
a wire extending between two roller arrangements, the wire being mounted so as to lie a predetermined distance above a surface when the roller arrangements are passed over the surface.
Each roller arrangement may comprise a single roller, the wire extending between the two rollers along the axis of rotation of the two rollers, or they may each comprise two rollers side by side having parallel axes of rotation, the wire being positioned between the two rollers and extending parallel to the axes of rotation of the two rollers between the two roller arrangements.